JP2017134912A - Ceramic heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic heater capable of suppressing increase in the value of resistance, due to crack occurring between a lead terminal having a coil and a solder material.SOLUTION: The ceramic heater includes a rod-like ceramic body 1, a resistor 2 embedded in the ceramic body 1, an electrode layer 3 provided on the surface of the ceramic body 1 and connected electrically with the resistor 2, a lead terminal 4 having a coil 41 formed by winding a metal wire multiple times around the ceramic body 1 to cover the electrode layer 3, and a solder material 5 for joining the electrode layer 3 and the coil 41 of the lead terminal 4. When viewing the coil 41 in the cross section in the longitudinal direction of the ceramic body 1, the solder material 5 is provided from the electrode layer 3 to the surface on the outside of the center of the metal wire constituting the coil 41.SELECTED DRAWING: Figure 1

Description

  The present invention is, for example, for a heater for ignition or flame detection in a combustion-type in-vehicle heating device, a heater for ignition of various combustion devices such as an oil fan heater, a heater for a glow plug of an automobile engine, and various sensors such as an oxygen sensor. The present invention relates to a heater used as a heater for heating a measuring instrument and a heater for measuring equipment.

  As a ceramic heater, a rod-shaped ceramic body, a resistor embedded in the ceramic body, an electrode layer provided on the surface of the ceramic body and electrically connected to the resistor, and an electrode around the ceramic body A device including a lead terminal having a coil portion in which a metal wire is wound a plurality of times so as to cover a layer and a brazing material that joins the electrode layer and the coil portion of the lead terminal is known (for example, a patent) References 1 and 2).

JP-A-8-264267 JP-A-10-32078

  For example, in ceramic heaters and glow plugs for diesel engines, when used in a state where high and low temperatures are repeated, the difference in thermal expansion between the coil portion of the lead terminal and the ceramic body causes a gap between the coil portion and the brazing material. A thermal stress is applied along the longitudinal direction of the ceramic body to cause a crack, which may develop and increase the resistance value.

  An object of the present invention is to provide a ceramic heater in which cracks are prevented from progressing between a coil portion of a lead terminal and a brazing material.

  The present invention provides a rod-shaped ceramic body, a resistor embedded in the ceramic body, an electrode layer provided on the surface of the ceramic body and electrically connected to the resistor, and the ceramic body. A lead terminal having a coil portion in which a metal wire is wound a plurality of times so as to cover the electrode layer, and a brazing material for joining the electrode layer and the coil portion of the lead terminal; When the coil portion is viewed in a cross section along the longitudinal direction of the ceramic body, the brazing material is provided from the electrode layer to a surface outside the center of the metal wire constituting the coil portion. This is a ceramic heater.

  According to the ceramic heater of the present invention, when a crack is generated between the coil portion and the brazing material and is about to progress, the progress can be suppressed.

(A) is a longitudinal cross-sectional view which shows an example of the ceramic heater of this embodiment, (b) is an enlarged view of the area | region A (principal part) shown to (a). It is a principal part expanded longitudinal sectional view of the other example of the ceramic heater of this embodiment. It is a principal part expanded longitudinal sectional view of the other example of the ceramic heater of this embodiment. It is a principal part expanded longitudinal sectional view of the other example of the ceramic heater of this embodiment. It is a principal part expanded longitudinal sectional view of the other example of the ceramic heater of this embodiment.

  Hereinafter, an example of the ceramic heater of the present embodiment will be described in detail with reference to the drawings.

  Fig.1 (a) is a longitudinal cross-sectional view which shows an example of the ceramic heater of this embodiment, FIG.1 (b) is an enlarged view of the area | region A (principal part) shown to Fig.1 (a).

  The ceramic heater shown in FIG. 1 includes a rod-shaped ceramic body 1, a resistor 2 embedded in the ceramic body 1, and an electrode layer provided on the surface of the ceramic body 1 and electrically connected to the resistor 2. 3, a lead terminal 4 having a coil portion 41 in which a metal wire is wound a plurality of times so as to cover the electrode layer 3 around the ceramic body 1, and the electrode layer 3 and the coil portion 41 of the lead terminal 4 are joined together. The brazing material 5 is provided, and when the coil portion 41 is viewed in a cross section along the longitudinal direction of the ceramic body 1, the brazing material 5 is outside the center of the metal wire constituting the coil portion 41 from the electrode layer 3. To the surface.

  The ceramic body 1 is formed in a rod shape. The length of the ceramic body 1 is, for example, 20 to 60 mm, and the diameter when the ceramic body 1 is circular in cross section is, for example, 2.5 to 5.5 mm.

  Examples of the material for forming the ceramic body 1 include ceramics having electrical insulation properties such as oxide ceramics, nitride ceramics, and carbide ceramics. Specifically, alumina ceramics, silicon nitride ceramics, aluminum nitride ceramics, silicon carbide ceramics, or the like can be used. In particular, silicon nitride ceramics are preferable in that silicon nitride, which is a main component, is excellent in terms of high strength, high toughness, high insulation, and heat resistance.

The ceramic body 1 may contain a compound of a metal element contained in the resistor 2. For example, when the resistor 2 contains tungsten or molybdenum, the ceramic body 1 has WSi ₂ or MoSi _2. May be included. By doing in this way, the thermal expansion coefficient of the silicon nitride ceramic which is a base material can be brought close to the thermal expansion coefficient of the resistor 2, and the durability of the ceramic heater can be improved.

  In the example shown in FIG. 1, the resistor 2 embedded in the ceramic body 1 has a folded portion having a folded shape in the longitudinal section on the tip side, and is near the center of the folded portion (the middle of the folded portion). The vicinity of the point) is the heat generating part that generates the most heat. The resistor 2 is a pair of linear portions on the rear end side from the folded portion, and is drawn out to the surface of the ceramic body 1 in the vicinity of the rear end of each linear portion. The shape of the cross section of the resistor 2 may be any shape such as a circle, an ellipse, or a rectangle.

As a material for forming the resistor 2, a material mainly composed of carbide, nitride, silicide or the like such as tungsten, molybdenum, or titanium can be used. When the ceramic body 1 is made of silicon nitride ceramics, tungsten carbide (WC) is one of the above materials in that it has a small difference in thermal expansion coefficient from the ceramic body 1, high heat resistance, and low specific resistance. Is excellent as a material of the resistor 2. Furthermore, when the ceramic body 1 is made of silicon nitride ceramics, the resistor 2 is preferably composed mainly of WC and the content of silicon nitride added thereto is 20% by mass or more. For example, in the ceramic body 1 made of silicon nitride ceramics, the conductor component that becomes the resistor 2 has a higher coefficient of thermal expansion than silicon nitride, and therefore is usually in a state where tensile stress is applied. On the other hand, since the resistor 2 contains silicon nitride, the coefficient of thermal expansion of the resistor 2 is brought close to the coefficient of thermal expansion of the ceramic body 1, and the coefficient of thermal expansion when the heater is raised and lowered is reduced. The stress due to the difference can be relaxed. Further, when the content of silicon nitride contained in the resistor 2 is 40% by mass or less, the resistance value of the resistor 2 can be made relatively small and stabilized. Therefore, the content of silicon nitride contained in the resistor 2 is preferably 20% by mass to 40% by mass.

  In addition, the resistor 2 is formed by using the same material for the folded portion on the front end side and the pair of linear portions on the rear end side. The resistance per unit length of the linear portion is larger than the folded portion by increasing the area larger than the cross-sectional area of the folded portion or reducing the content of the forming material of the ceramic body 1 contained in the linear portion. The value may be reduced. Furthermore, the resistor 2 is not limited to the configuration including the folded portion having the shape shown in FIG. 1 and a pair of linear portions on the rear end side, and may be a pattern in which the folded portion is folded repeatedly a plurality of times. Two patterns of the shape shown in FIG. 1 may be laminated.

  On the surface of the ceramic body 1, an electrode layer 3 electrically connected to the resistor 2 embedded in the ceramic body 1 is provided. The electrode layer 3 is made of, for example, molybdenum (Mo) or tungsten (W), and has a thickness of, for example, 50 to 300 μm. The electrode layer 3 may be provided only in the portion of the surface of the ceramic body 1 where the resistor 2 is drawn out and in the vicinity thereof, and the entire electrode layer 3 is opposed to a coil portion 41 constituting a lead terminal 4 described later. It may be provided over the circumference. In the example shown in FIG. 1, there are two portions from which the resistor 2 is drawn, and the electrode layer 3 is provided over the entire circumference in each portion. In addition, since the site | parts where the two resistor 2 was pulled out exist in a different position regarding a longitudinal direction, the electrode layer 3 can be provided so that it may not electrically conduct mutually. Further, the electrode layer 3 may have a surface provided with a plating layer made of, for example, Ni-B or Au.

  Around the ceramic body 1, there is provided a lead terminal 4 having a coil portion 41 in which a metal wire is wound a plurality of times so as to cover the electrode layer 3. The lead terminal 4 is made of, for example, Ni, Fe, a Ni-based heat-resistant alloy, or the like, and is made of, for example, a metal wire having a diameter of 0.5 to 2.0 mm. In the example shown in FIG. 1, two lead terminals 4 are provided. Each lead terminal 4 has a coil part 41 in which a metal wire is wound a plurality of times, and the coil part 41 is usually configured by winding a metal wire 2-6 times. The electrode layer 3 and the coil part 41 of the lead terminal 4 are electrically connected via a brazing material 5 made of, for example, Ag, Cu, Au, or the like.

  And when the coil part 41 is seen in the cross section along the longitudinal direction of the ceramic body 1, the brazing | wax material 5 is provided from the electrode layer 3 to the surface outside the center of the metal wire which comprises the coil part 41. FIG. In other words, when the coil portion 41 is viewed in a cross section along the longitudinal direction of the ceramic body 1, the boundary between the coil portion 41 of the lead terminal 4 and the brazing material 5 is more than the center of the metal wire constituting the coil portion 41. It is to the outside surface. In FIG. 1B, a line connecting the centers of the metal wires constituting the coil portion 41 is indicated by a one-dot chain line B, and to the outside of the one-dot chain line B (on the side opposite to the electrode layer 3 side). It is shown that a brazing material 5 is provided.

  According to such a configuration, a crack is generated between the coil portion 41 and the brazing filler metal 5 due to thermal expansion caused by rapid temperature rise, and this crack tends to propagate along the boundary between the coil portion 41 and the brazing filler metal 5. When this is done, the progress direction is greatly inclined, so that the progress can be suppressed. In particular, on the outer side (the outer side in the longitudinal direction) of the metal wire at the end of the plurality of metal wires, the brazing material 5 greatly wraps around the surface outside the center of the metal wire, so that cracks generated inside are generated. Propagation to the end of the boundary between the coil portion 41 and the brazing material 5 can be suppressed. Therefore, an increase in resistance value can be suppressed over a long period.

  Here, as shown in FIG. 2, when the coil portion 41 is viewed in a cross section along the longitudinal direction of the ceramic body 1, there are a plurality of boundaries where the adjacent metal wires are in contact with each other and the outside of each boundary. The brazing material 5 is provided on the surface, and the thickness of the brazing material 5 provided on the outer surface of at least one boundary is greater than the thickness of the brazing material 5 provided on the outer surface of the other boundary. Is good. In FIG. 2, there are three boundaries between adjacent metal lines, and the thickness t1 of the brazing material 5 on the boundary 42b is the thickness t2 of the brazing material 5 on the boundary 42a and the boundary 42c. It is thicker than.

  There are a plurality of borders between adjacent metal wires and the metal wires, and the brazing material 5 is provided on the outer surface of each border, so that the adjacent metal wires and metal wires are located on the inner side of the border where they are in contact. Therefore, it is possible to suppress the occurrence of cracks at the boundary between the brazing filler metal 5 and the coil portion 41. Furthermore, since the thickness of the brazing material 5 provided on the outer surface of at least one boundary is larger than the thickness of the brazing material 5 provided on the outer surface of the other boundary, the following effects can be obtained. The part where the brazing material 5 is thick (the part where the thickness is t1) is stronger in bonding strength than the part where the thickness is thin (the part where the thickness is t2), and the brazing material 5 is prevented from peeling off. On the other hand, the thin part (part of thickness t2) of the brazing material 5 is more easily deformed than the thick part (part of thickness t1), and the stress is dispersed in the twist direction of the coil portion 41 to cause stress in the longitudinal direction. The effect of suppressing the development of cracks is reduced.

  In addition, when the thickness t2 of the thin part of the brazing material 5 is, for example, 100 to 500 μm, the thickness t1 of the thick part is set to be, for example, 50 to 300 μm thicker than the thickness t2.

  Also, as shown in FIG. 3, there is a gap 43 between adjacent metal wires constituting the coil portion 41, and the brazing material 5 located between the metal wires is outside the center of the metal wire constituting the coil portion 41. The surface may be provided. According to this structure, it can suppress that the brazing material 5 absorbs the stress when a metal wire thermally expands, and a crack arises more. The gap 43 is set to, for example, 10 μm to 100 μm.

  Moreover, as shown in FIG. 4, when the coil part 41 is seen in the cross section along the longitudinal direction of the ceramic body 1, the thickness of the brazing material 5 located between at least one metal wire is located between other metal wires. It may be thicker than the thickness of the brazing filler metal 5. In FIG. 4, there are three gaps 43 between adjacent metal lines, and the thickness t3 of the brazing material 5 located between the metal lines with the gap 43b is between the metal lines with the gap 43a and It is thicker than the thickness t4 of the brazing material 5 located between the metal wires with the gap 43c.

  Even with this configuration, the thick part of the brazing material 5 has stronger bonding strength than the thin part, and the effect of suppressing the peeling of the brazing material 5 can be achieved. On the other hand, the thin part of the brazing material 5 is more easily deformed than the thick part, and an effect of reducing the stress in the longitudinal direction by dispersing the stress in the twist direction of the coil portion 41 can be achieved.

  In addition, when the thickness t4 (distance from the electrode layer 3 to the surface of the brazing material 5) of the thin part of the brazing material 5 is, for example, 200 to 1000 μm, the thickness t3 of the thick part (from the electrode layer 3 to the brazing material 5). The distance to the surface) is set to be, for example, 100 to 600 μm thicker than the thickness t4.

  Further, as shown in FIG. 5, the brazing material 5 covers the entire outer surface of the coil portion 41, and the outer surface of the brazing material 5 has an unevenness along the outer surface shape of the metal wire constituting the coil portion 41. It may be.

  When the temperature of the ceramic heater is rapidly raised, the temperature gradually rises from the metal wire on the tip side constituting the coil portion 41 to start thermal expansion, and between adjacent metal wires when viewed in cross section. However, although a difference in thermal expansion occurs and stress in the longitudinal direction is generated, the brazing material 5 covers the entire outer surface of the coil portion 41, so that the brazing material 5 has higher thermal conductivity than the coil portion 41. Therefore, a part of the heat is transmitted through the brazing material 5 and is dissipated from the surface of the brazing material 5. Therefore, the stress produced by the difference in thermal expansion between adjacent metal wires can be reduced. In addition, since the outer surface of the brazing material 5 has an uneven shape along the outer surface shape of the metal wire, the recess 51 is easily deformed. It is possible to reduce the stress in the direction and suppress the development of cracks. In addition, the thickness of the brazing material 5 in the example shown in FIG. 5 is set to 100 to 500 μm, for example.

  A method for manufacturing the ceramic heater of the present embodiment will be described.

First, a ceramic powder serving as a raw material of the ceramic body 1 is prepared by adding a sintering aid such as SiO ₂ , CaO, MgO, ZrO ₂ to ceramic powder such as alumina, silicon nitride, aluminum nitride, silicon carbide. . For example, when the ceramic body 1 is made of silicon nitride ceramic, 3 to 12% by mass of Y ₂ O ₃ , Yb ₂ O ₃ , Er ₂ O _3, etc. as a sintering aid with respect to silicon nitride as the main component. Rare earth element oxide, 0.5 to 3% by mass of Al ₂ O ₃ , and further SiO ₂ is mixed so that the amount of SiO ₂ contained in the sintered body is 1.5 to 5% by mass.

  Next, the ceramic powder is press-molded to produce a molded body, or the ceramic powder is prepared into a ceramic slurry and molded into a sheet shape to produce a ceramic green sheet. Here, the obtained molded body or ceramic green sheet becomes the ceramic body 1 in a halved state.

  Next, a conductive paste pattern to be the resistor 2 is formed on one main surface of the obtained molded body or ceramic green sheet by screen printing or the like. Here, as a material of the conductive paste, a refractory metal such as W, Mo, Re or the like that can be fired simultaneously with the molded body to be the ceramic body 1 is a main component. What was prepared by preparing and kneading a binder, an organic solvent, etc. can be used.

  At this time, the heating position and resistance value of the resistor 2 are set to desired values by changing the length, line width, distance and interval of the folded pattern of the conductive paste according to the application of the ceramic heater. Set.

  By superimposing a molded body of the same material on which the conductive paste is not printed on the molded body on which the pattern of the conductive paste is formed, a molded body on which the pattern of the conductive paste is formed is obtained.

  Next, the obtained green body is fired at 1500 to 1800 ° C., for example, under a pressure of 30 to 50 MPa, whereby the ceramic body 1 in which the resistor 2 is embedded can be manufactured. The firing is preferably performed in an inert gas atmosphere or a reducing atmosphere. Moreover, it is preferable to bake in the state which applied the pressure.

Next, the obtained sintered body is processed into a rod-like or plate-like shape, and the electrode layer 3 is formed by screening printing, followed by baking in a vacuum furnace and then Ni-B plating. Furthermore, for example, a lead wire 4 is prepared by forming a metal wire containing Ni having a diameter of 1.0 mm as a main component into a coil shape by using, for example, a forming machine, and cutting the lead wire 4. A lead terminal 4 is fitted into a processed product (ceramic body 1 in which a resistor 2 is embedded and an electrode layer 3 is provided on the surface), and after positioning with a carbon jig or the like, for example, 700 ° C. to 900 ° C. Braze in a vacuum furnace. As a result, the brazing material 5 as shown in FIG. 1 is provided from the electrode layer 3 to a surface outside the center of the metal wire constituting the coil portion 41. By appropriately adjusting the amount of the brazing material 5 or the like, the thickness of the brazing material 5 provided on at least one boundary as shown in FIG. 2 is larger than the thickness of the brazing material 5 provided on the other boundary. It can be set as the structure which is thick. Moreover, when forming the coil portion 41, a gap (for example, 10 μm to 90 μm) is provided between the adjacent metal wires and the metal wires, whereby a configuration as shown in FIG. The structure as shown in FIG. 4 can be obtained by appropriately adjusting the amount of the light source. Further, by increasing the amount of the brazing material 5 and brazing at a higher temperature of the vacuum furnace, for example, by about 50 ° C., a configuration as shown in FIG. 5 can be obtained.

  Examples of the present invention will be described.

First, as a raw material of the ceramic body, 85% by mass of silicon nitride powder, 10% by mass of Yb ₂ O ₃ powder as a sintering aid, 3.5% by mass of MoSi ₂ powder, and 1.5% by mass of aluminum oxide powder The raw material powder was produced by mixing. Thereafter, a half-shaped molded body to be a ceramic body was produced by press molding using this raw material powder.

Next, as a conductive paste serving as a resistor, 70% by mass of tungsten carbide (WC) powder is mixed with 29.95% by mass of silicon nitride powder, and 0.05% by mass of metal compound Cr ₃ C ₂ as an additive. It was prepared by adding an organic solvent and a solvent. Here, the silicon nitride powder mixed with the tungsten carbide (WC) powder was mixed with 0.1% by mass of Yb ₂ O ₃ powder as an auxiliary agent.

  Next, the conductive paste was applied in the shape shown in FIG. 1 to the surface of the half-shaped molded body to be a ceramic body by a screen printing method.

  Next, after putting the obtained molded body into a cylindrical carbon mold, it was sintered by hot press firing at a temperature of 1700 ° C. and a pressure of 35 MPa in a reducing atmosphere.

  Next, the obtained sintered body was polished into a cylindrical shape having a diameter of 4 mm and a total length of 40 mm, and the exposed portion of the resistor led to the surface of the ceramic body and its surroundings were Ag powder mass 80%, Cu powder mass 15 %, Ti powder 5% A suitable organic solvent and solvent-added electrode layer paste was screen printed and then baked at 900 ° C. for 3 hours using a vacuum furnace. Then, 2 μm of NI-b plating was applied to form an electrode layer.

  Further, a metal wire having a diameter of 1.0 mm, which is mainly composed of Ni, was formed into a coil shape by using a forming machine so as to be wound four times with an inner diameter of 4.5 mm. The gap between the metal wires of the coiled portion was set to 5 μm or less. The obtained lead terminal was fitted in an appropriate position on the side surface of the ceramic body, and brazed in a vacuum furnace at 800 ° C. using a brazing material consisting of 85% Au powder mass and 15% Cu powder mass. A ceramic heater (sample 1) having a form as shown in FIG. 2 as an example of the invention was produced. On the other hand, using the same lead terminal and the same brazing material as in sample 1, brazing was performed at 800 ° C. under normal pressure, and the brazing material remained inside the center of the metal wire constituting the coil portion from the electrode layer. A ceramic heater (sample 2) as a comparative example was produced.

  A voltage was applied to each prepared heater of the sample to 1500 ° C., and intermittent energization was performed. Specifically, energization at 1500 ° C. ± 25 ° C. is continued for 1 minute, and energization is stopped for 1 minute to perform air cooling. This was defined as 1 cycle, and intermittent energization was performed for 10,000 cycles.

Then, the resistance change rate was compared by measuring the initial resistance value and the resistance value after 10,000 cycles. As for the resistance change, the tip of the ceramic heater was immersed in a constant temperature bath at 25 ° C. and stabilized at 25 ° C., then the initial resistance value and the resistance value after the test were measured, and the resistance change rate during that time was evaluated.

  Further, after the end of 10,000 cycles, it was cut into a cross section in the longitudinal direction including the coil portion and the brazing material, and the vicinity of the boundary between the coil portion and the brazing material was observed at SEM 1000 times.

  As a result, the ceramic heater of Sample 2 as a comparative example was confirmed to have a plurality of cracks in the brazing material, and the resistance change rate after the end of 10,000 cycles was 15%.

  On the other hand, in the ceramic heater of Sample 1 which is an embodiment of the present invention, the rate of change in resistance after 10,000 cycles was suppressed to 0.03%, and it was confirmed by SEM observation that no crack was generated. It was.

1: Ceramic body 2: Resistor 3: Electrode layer 4: Lead terminal 41: Coil portions 42a, 42b, 42c: Boundaries 43, 43a, 43b, 43c: Gap 5: Brazing material 51: Recess

Claims (5)

A rod-shaped ceramic body; a resistor embedded in the ceramic body; an electrode layer provided on a surface of the ceramic body and electrically connected to the resistor; and the electrode around the ceramic body A lead terminal having a coil portion in which a metal wire is wound a plurality of times so as to cover the layer, and a brazing material for joining the electrode layer and the coil portion of the lead terminal,
When the coil portion is viewed in a cross section along the longitudinal direction of the ceramic body, the brazing material is provided from the electrode layer to a surface outside the center of the metal wire constituting the coil portion. Ceramic heater.   When the coil portion is viewed in a cross section along the longitudinal direction of the ceramic body, there are a plurality of boundaries where adjacent metal wires and metal wires are in contact with each other, and the brazing material is provided on the outer surface of each boundary. The thickness of the brazing material provided on the outer surface of at least one boundary is thicker than the thickness of the brazing material provided on the outer surface of the other boundary. Ceramic heater.   There is a gap between adjacent metal wires constituting the coil portion, and the brazing material located between the metal wires is provided to a surface outside the center of the metal wire constituting the coil portion. The ceramic heater according to claim 1.   When the coil portion is viewed in a cross section along the longitudinal direction of the ceramic body, the thickness of the brazing material located between at least one metal wire is larger than the thickness of the brazing material located between other metal wires. The ceramic heater according to claim 3, wherein   The brazing material covers the entire outer surface of the coil portion, and the outer surface of the brazing material has a shape having irregularities along the outer surface shape of the metal wire constituting the coil portion. The ceramic heater according to any one of claims 1 to 4.

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